Re: [PATCH 5/9] fs: remove various compat readv/writev helpers

Al Viro
2020-09-23T14:59:21Z

On Wed, Sep 23, 2020 at 04:32:51PM +0200, Christoph Hellwig wrote:
> On Wed, Sep 23, 2020 at 03:25:49PM +0100, Al Viro wrote:
> > On Wed, Sep 23, 2020 at 08:05:43AM +0200, Christoph Hellwig wrote:
> > > COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
> > > - const struct compat_iovec __user *,vec,
> > > + const struct iovec __user *, vec,
> >
> > Um... Will it even compile?
> >
> > > #ifdef __ARCH_WANT_COMPAT_SYS_PREADV64
> > > COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
> > > - const struct compat_iovec __user *,vec,
> > > + const struct iovec __user *, vec,
> >
> > Ditto. Look into include/linux/compat.h and you'll see
> >
> > asmlinkage long compat_sys_preadv64(unsigned long fd,
> > const struct compat_iovec __user *vec,
> > unsigned long vlen, loff_t pos);
> >
> > How does that manage to avoid the compiler screaming bloody
> > murder?
>
> That's a very good question. But it does not just compile but actually
> works. Probably because all the syscall wrappers mean that we don't
> actually generate the normal names. I just tried this:
>
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -468,7 +468,7 @@ asmlinkage long sys_lseek(unsigned int fd, off_t offset,
> asmlinkage long sys_read(unsigned int fd, char __user *buf, size_t count);
> asmlinkage long sys_write(unsigned int fd, const char __user *buf,
> size_t count);
> -asmlinkage long sys_readv(unsigned long fd,
> +asmlinkage long sys_readv(void *fd,
>
> for fun, and the compiler doesn't care either..

Try to build it for sparc or ppc...